Selected methylol-substituted trihydroxybenzophenones and their use in phenolic resin compositions and processes of forming resist images

ABSTRACT

A methylol-substituted trihydroxybenzophenone of the formula (I): ##STR1## This methylol-substituted trihydroxybenzophenone may be reacted with selected phenolic monomers during or after the formation of a phenolic novolak resin thereby said resin having at least one unit of formula (II): ##STR2## wherein R and R 1  are individually selected from hydrogen, a lower alkyl group having 1 to 4 carbon atoms or a lower alkoxy group having 1 to 4 carbon atoms.

This application is a division of application Ser. No. 07/654,841, filedFeb. 13, 1991, now U.S. Pat. No. 5,177,172 issued on Jan. 5, 1993, whichis a division of application Ser. No. 07/200,676 filed May 31, 1988 nowU.S. Pat. No. 5,002,851 issued on May 26, 1991.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to selected methylol-substitutedtrihydroxybenzophenones as novel compositions of matter. The presentinvention relates to selected phenolic resins containing at least oneunit which is a condensation product of the selectedmethylol-substituted trihydroxbenzophenones and selected phenolicmonomers. Furthermore, the present invention relates to light-sensitivecompositions useful as positive-working photoresist compositions,particularly, those containing these phenolic resins ando-quinonediazide photosensitizers. Still further, the present inventionalso relates to substrates coated with these light-sensitivecompositions as well as the process of coating, imaging and developingthese light-sensitive mixtures on these substrates.

2. Description of Related Art

Photoresist compositions are used in microlithographic processes formaking miniaturized electronic components such as in the fabrication ofintegrated circuits and printed wiring board circuitry. Generally, inthese processes, a thin coating or film of a photoresist composition isfirst applied to a substrate material, such as silicon wafers used formaking integrated circuits or aluminum or copper plates of printedwiring boards. The coated substrate is then baked to evaporate anysolvent in the photoresist composition and to fix the coating onto thesubstrate. The baked coated surface of the substrate is next subjectedto an image-wise exposure of radiation. This radiation exposure causes achemical transformation in the exposed areas of the coated surface.Visible light, ultraviolet (UV) light, electron beam and X-ray radiantenergy are radiation types commonly used today in microlithographicprocesses. After this image-wise exposure, the coated substrate istreated with a developer solution to dissolve and remove either theradiation-exposed or the unexposed areas of the coated surface of thesubstrate.

There are two types of photoresist compositions--negative-working andpositive-working. When negative-working photoresist compositions areexposed image-wise to radiation, the areas of the resist compositionexposed to the radiation become less soluble to a developer solution(e.g. a cross-linking reaction occurs) while the unexposed areas of thephotoresist coating remain relatively soluble to a developing solution.Thus, treatment of an exposed negative-working resist with a developersolution causes removal of the non-exposed areas of the resist coatingand the creation of a negative image in the photoresist coating, andthereby uncovering a desired portion of the underlying substrate surfaceon which the photoresist composition was deposited. On the other hand,when positive-working photoresist compositions are exposed image-wise toradiation, those areas of the resist composition exposed to theradiation become more soluble to the developer solution (e.g. arearrangement reaction occurs) while those areas not exposed remainrelatively insoluble to the developer solution. Thus, treatment of anexposed positive-working resist with the developer solution causesremoval of the exposed areas of the resist coating and the creation of apositive image in the photoresist coating. Again, a desired portion ofthe underlying substrate surface is uncovered.

After this development operation, the now partially unprotectedsubstrate may be treated with a substrate-etchant solution or plasmagases and the like. This etchant solution or plasma gases etch theportion of the substrate where the photoresist coating was removedduring development. The areas of the substrate where the photoresistcoating still remains are protected and, thus, an etched pattern iscreated in the substrate material which corresponds to the photomaskused for the image-wise exposure of the radiation. Later, the remainingareas of the photoresist coating may be removed during a strippingoperation, leaving a clean etched substrate surface. In some instances,it is desirable to heat treat the remaining resist layer after thedevelopment step and before the etching step to increase its adhesion tothe underlying substrate and its resistance to etching solutions.

Positive-working photoresist compositions are currently favored overnegative-working resists because the former generally have betterresolution capabilities and pattern transfer characteristics.

Photoresist resolution is defined as the smallest feature which theresist composition can transfer from the photomask to the substrate witha high degree of image edge acuity after exposure and development. Inmany manufacturing applications today, resist resolution on the order ofone micron or less are necessary.

In addition, it is generally desirable that the developed photoresistwall profiles be near vertical relative to the substrate. Suchdemarcations between developed and undeveloped areas of the resistcoating translate into accurate pattern transfer of the mask image ontothe substrate.

One drawback with positive-working photoresists known heretofore istheir limited resistance to thermal image deformation. This limitationis becoming an increasing problem because modern processing techniquesin semiconductor manufacture (e.g. plasma etching, ion bombardment)require photoresist images which have higher image deformationtemperatures (e.g. 1500° C.-200° C.). Past efforts to increase thermalstability (e.g. increased molecular weight of the resin) generallycaused significant decrease in other desirable properties (e.g.decreased photospeed, diminished adhesion, or reduced contrast, poorerdeveloper dissolution rates), or combinations thereof].

Accordingly, there is a need for improved positive-working photoresistformulations which produce images that are resistant to thermaldeformation at temperatures of about 150° to 200° C. while maintainingthe other desired properties (e.g. developer dissolution rates) atsuitable levels. The present invention is believed to be an answer tothat need.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to selectedmethylol-substituted trihydroxybenzophenones of the formula (I):##STR3##

Moreover the present invention is directed to a phenolic novolak resincomprising at least one unit of formula (II): ##STR4## wherein R and R₁are individually selected from hydrogen, a lower alkyl group having 1 to4 carbon atoms and a lower alkoxy having I to 4 carbon atoms and saidunit or units of formula (II) are made by condensing themethylol-substituted trihydroxybenzophenone of formula (I) with selectedphenolic monomer units of formula (III): ##STR5## wherein R and R₁ aredefined above.

Moreover, the present invention is directed to a light-sensitivecomposition useful as a positive photoresist comprising an admixture ofo-quinonediazide compound and binder resin comprising at least one unitof the formula (II), above; the amount of said o-quinonediazide compoundor compounds being about 5% to about 40% by weight and the amount ofsaid binder resin being about 60% to 95% by weight, based on the totalsolid content of said light-sensitive composition.

Still further, the present invention also encompasses the process ofcoating substrates with these light-sensitive compositions and thenimaging and developing these coated substrates.

Also further, the present invention encompasses said coated substrates(both before and after imaging) as novel articles of manufacture.

DETAILED DESCRIPTION

The selected methylol-substituted trihydroxybenzophenones of formula (I)are made by reacting the corresponding trihydroxybenzophenone withformaldehyde under alkaline pH conditions. This reaction is illustratedbelow in reaction equation (A) wherein the trihydroxybenzophenone is2,3,4-trihydroxybenzophenone and the alkali employed is NaOH and5-methylol-2,3,4-trihydroxybenzophenone is made: ##STR6## It should benoted that when 2,3,4-trihydroxybenzophenone is employed as thereactant, the reaction occurs almost completely at the 5-position of thetrihydroxyphenyl ring. Other isomeric reactions are insignificant. Thereason for the selectivity of this particular reaction is the relativeelectronic activation of the 5-position by the hydroxyl groups on thering; however, the present invention is not to be limited to anyparticular reactants or process limitation for this particular type ofreaction.

In making the class of compounds of the present invention, theprecursors are preferably reacted at about a 1:1 mole ratio. Thepreferred reaction temperature is about 40°-500° C. for about 2.5 hoursor less at atmospheric pressure. Excess reaction time may causeundesirable polymerization of the intended product. This reactionpreferably occurs at an alkaline pH of greater than 7. The pH may becontrolled by the addition of specific amounts of alkaline compounds(e.g. NAOH, KOH, Na₂ CO₃ and the like). The intended product may berecovered from the reaction mixture by mixing the reaction mixture withacidified water and thus precipitating the product in solid form.

The phenolic resins containing one or more units of formula (II) aboveare preferably made by reacting the methylol-substitutedtrihydroxybenzophenone of formula (I), above, and the selected phenolicmonomers having units of formula (III) with formaldehyde under usualnovolak-making conditions. Generally, this reaction occurs in thepresence of an acid catalyst. Suitable acid catalysts include thosecommonly employed in acid condensation-type reactions such as HCl, H₃PO₄, H₂ SO₄, oxalic acid, maleic acid, maleic anhydride and organicsulfonic acids (e.g. p-toluene sulfonic acid). The most preferred acidcatalyst is oxalic acid. Generally, it is also preferred to carry outthe condensation reaction of compounds of formulae (I) with (III) eithersimultaneously or after the novolak polymerization in the presence of anaqueous medium or an organic solvent. Suitable organic solvents includeethanol, tetrahydrofuran, cellosolve acetate, 1-methoxy-2-propanol and2-ethoxy ethanol. Preferred solvents are water-soluble solvents such asethanol, 1-methoxy-2-propanol and 2-ethoxy ethanol.

The mole ratio of the methylol-substituted trihydroxybenzophenone to thetotal of the other phenolic compounds (preferably, a combination ofmeta- and para-cresols) is generally from about 0.1:99.9 to 20:80; morepreferably, about 5:95 to about 10:90.

The methylolated trihydroxybenzophenone of formula (I) predominatelyreacts in the para-position on the phenolic molecules as illustrated informula (III), above. For example, this trihydroxybenzophenone compoundwill predominately react with phenol or ortho- or meta-cresol, but lessfavorably with para-substituted phenolic molecules. The thus preparednovolaks containing the units of formula (II), above, have showedgreater dissolution rates in aqueous alkaline developers thancorresponding novolaks prepared without these units. Furthermore,light-sensitive compositions prepared with novolaks containing theseunits of formula (II) also showed good thermal stability due to theirhigher molecular weight and high resolution images. It is also believedthat the presence of the units of formula (II) in the novolak resinsignificantly reduce the degree of branching of the novolak and provideunhindered hydroxyl (OH) groups for improved solubility properties andchemical reactivity.

In making the present class of resins, the precursors, namely, thetrihydroxybenzophenones of formula (I) and the phenolic monomers (mostpreferably, a mixture of meta- and para-cresols) are preferably placedin a reaction vessel with formaldehyde. The reaction mixture usuallyalso contains an acid catalyst and solvent as noted above. The mixtureis then preferably heated to a temperature in the range from about 60°C. to about 120° C., more preferably from about 65° C. to about 95° C.,for both the novolak-forming condensation polymerization reaction andthe separate phenolic resin-trihydroxybenzophenone condensation reactionto occur. If an aqueous medium is used instead of an organic solvent,the reaction temperature is usually maintained at reflux, e.g. about 95°C. to 110° C. The reaction time will depend on the specific reactantsused and the ratio of formaldehyde to phenolic monomers. The mole ratioof formaldehyde to total phenolic moieties is generally less than about1:1. Reaction times from 3 to 20 hours are generally suitable.Alternatively, the trihydroxybenzophenones of formula (I) may be firstreacted to the phenolic monomers of formula (III) without the presenceof formaldehyde. In such cases, the condensation product of formula (II)is made and such condensation products may then be reacted withformaldehyde along with other phenolic monomers to make the novolakresins of the present invention.

The most preferred methylol-substituted trihydroxybenzophenone is5-methylol-2,3,4-trihydroxybenzophenone as shown above in formula (A).The most preferred phenolic monomers is a mixture of meta-cresol andpara-cresol having a mole ratio ranging from about 70:30 to about 30:70,respectively.

Branched and unbranched novolak resins made from this mixture of meta-and para-cresols will thus include the following types of repeatedphenolic units: (1) units of formula (II) above; (2) meta-cresol unitsof the formula (IV), (IVA) and (IVB): ##STR7## and para-cresol units offormula (V): ##STR8##

Regardless of the presence or absence of the further units of formulae(IV) and (V), the resins of the present invention preferably have amolecular weight of from about 500 to about 25,000, more preferably fromabout 750 to about 20,000. The preferred resins have from about 0.1% toabout 30%, more preferably about 5% to 10% by moles of the units offormula (II).

The above-discussed resins of the present invention may be mixed withphotoactive compounds to make light-sensitive mixtures which are usefulas positive acting photoresists. The preferred class of photoactivecompounds (sometimes called light sensitizers) is o-quinonediazidecompounds particularly esters derived from polyhydric phenols,alkylpolyhydroxyphenones, aryl-polyhydroxyphenones, and the like whichcan contain up to six or more sites for esterification. The mostpreferred o-quinonediazide esters are derived from2-diazo-1,2-dihydro-1-oxonaphthlene-4-sulfonic acid and2-diazo-1,2-dihydro-1-oxo-naphthalene-5-sulfonic acid.

Specific examples include resorcinol1,2-naphthoquinonediazide-4-sulfonic acid esters; pyrogallol1,2-naphthoquinonediazide-5-sulfonic acid esters,1,2-quinonediazidesulfonic acid esters of (poly)hydroxyphenyl alkylketones or (poly)hydroxyphenyl aryl ketones such as 2,4-dihydroxyphenylpropyl ketone 1,2-benzoquinonediazide-4-sulfonic acid esters,2,4,dihydroxyphenyl hexyl ketone 1,2-naphthoquinonediazide-4-sulfonicacid esters, 2,4-dihydroxybenzophenone1,2-naphthoquinonediazide-5-sulfonic acid esters, 2,3,4-trihydroxyphenylhexyl ketone, 1,2-naphthoquinonediazide-4-sulfonic acid esters,2,3,4-trihydroxybenzophenone 1,2-naphthoquinonediazide-4-sulfonic acidesters, 2,3,4-trihydroxybenzophenone1,2-naphthoquinonediazide-5-sulfonic acid esters,2,4,6-trihydroxybenzophenone 1,2-naphthoquinonediazide-4-sulfonic acidesters, 2,4,6-trihydroxybenzophenone1,2-naphthoquinonediazide-5-sulfonic acid esters,2,2',4,4'-tetrahydroxybenzophenone 1,2-naphthoquinonediazide-5-sulfonicacid esters, 2.3.4,4'-tetrahydroxy-benzophenone1,2-naphthoquinonediazide-5-sulfonic acid esters,2,3,4,4'-tetrahydroxybenzophenone 1,2-naphthoquinonediazide-4-sulfonicacid esters, 2,2',3,4',61'-pentahydroxybenzophenone1,2-naphthoquinonediazide-5-sulfonic acid esters and2,3,3',4,4',5'-hexahydroxybenzophenone1,2-naphthoquinonediazide-5-sulfonic acid esters;1,2-quinonediazidesulfonic acid esters ofbis[(poly)hydroxyphenyl]alkanes such as bis(p-hydroxyphenyl)methane1,2-naphthoquinonediazide-4-sulfonic acid esters,bis(2,4-dihydroxyphenyl)methane 1,2-naphthoquinone-diazide-5-sulfonicacid esters, bis(2,3,4-trihydroxy-phenyl)methane1,2-naphthoquinonediazide-5-sulfonic acid esters,2,2-bis(p-hydroxyphenyl)propane 1,2-naphthoquinonediazide-4-sulfonicacid esters, 2,2-bis(2,4-dihydroxyphenyl)propane1,2-naphthoquinonediazide-5-sulfonic acid esters and2,2-bis(2,3,4-trihydroxyphenyl)propane1,2-naphthoquinonediazide-5-sulfonic acid esters. Besides the1,2-quinonediazide compounds exemplified above, there can also be usedthe 1,2-quinonediazide compounds described in J. Kosar, "Light-SensitiveSystems", 339-352 (1965), John Wiley Sons (New York) or in S. DeForest,"Photoresist", 50, (1975), MacGraw-Hill, Inc. (New York). In addition,these materials may be used in combinations of two or more. Further,mixtures of substances formed when less than all esterification sitespresent on a particular polyhydric phenol, alkyl-polyhydroxyphenone,arylpolyhydroxyphenone and the like have combined with o-quinonediazidesmay be effectively utilized in positive acting photoresists.

Of all the 1,2-quinonediazide compounds mentioned above,1,2-naphthoquinonediazide-5-sulfonic acid di-, tri-, tetra-, penta- andhexa-esters of polyhydroxy compounds having at least 2 hydroxyl groups,i.e. about 2 to 6 hydroxyl groups, are most preferred.

Among these most preferred 1,2-naphthoquinone-5-diazide compounds are2,3,4-trihydroxybenzophenone 1,2-naphthoquinonediazide-5-sulfonic acidesters, 2,3,4,4'-tetrahydroxybenzophenone1,2-naphthoquinonediazide-5-sulfonic acid esters, and2,2',4,4'-tetrahydroxybenzophenone 1,2-naphthoquinonediazide-5-sulfonicacid esters. These 1,2-quinonediazide compounds may be used alone or incombination of two or more.

The proportion of the light sensitizer compound in the light-sensitivemixture may preferably range from about 5 to about 40%, more preferablyfrom about 10 to about 25% by weight of the non-volatile (e.g.non-solvent) content of the light-sensitive mixture. The proportion oftotal binder resin of this present invention in the light-sensitivemixture may preferably range from about 60 to about 95%, morepreferably, from about 75 to 90% of the non-volatile (e.g. excludingsolvents) content of the light-sensitive mixture.

These light-sensitive mixtures may also contain conventional photoresistcomposition ingredients such as other resins, solvents, actinic andcontrast dyes, anti-striation agents, plasticizers, speed enhancers, andthe like. These additional ingredients may be added to the binder resinand sensitizer solution before the solution is coated onto thesubstrate.

Other binder resins may also be added beside the resins of the presentinvention mentioned above. Examples include phenolic-formaldehyderesins, cresol-formaldehyde resins, phenol-cresol-formaldehyde resinsand polvinylphenol resins commonly used in the photoresist art. If otherbinder resins are present, they will replace a portion of the binderresins of the present invention. Thus, the total amount of the binderresin in the light-sensitive composition will be from about 60% to aout95% by weight of the total non-volatile solids content of thelight-sensitive composition.

The resins and sensitizers may be dissolved in a solvent or solvents tofacilitate their application to the substrate. Examples of suitablesolvents include methoxyacetoxy propane, ethyl cellosolve acetate,n-butyl acetate, xylene, ethyl lactate, propylene glycol alkyl etheracetates, or mixtures thereof and the like. The preferred amount ofsolvent may be from about 50% to about 500%, or higher, by weight, morepreferably, from about 100% to about 400% by weight, based on combinedresin and sensitizer weight.

Actinic dyes help provide increased resolution on highly reflectivesurfaces by inhibiting back scattering of light off the substrate. Thisback scattering causes the undesirable effect of optical notching,especially on a substrate topography. Examples of actinic dyes includethose that absorb light energy at approximately 400-460 nm [e.g. FatBrown B (C.I. No. 12010); Fat Brown RR (C.I. No. 11285);2-hydroxy-1,4-naphthoquinone (C.I. No. 75480) and Quinoline Yellow A(C.I. No. 47000)] and those that absorb light energy at approximately300-340 nm [e.g. 2,5-diphenyloxazole (PPO-Chem. Abs. Reg. No. 92-71-7)and 2-(4-biphenyl)-6-phenyl-benzoxazole (PBBO-Chem. Abs. Reg. No.17064-47-0)]. The amount of actinic dyes may be up to ten percent weightlevels, based on the combined weight of resin and sensitizer.

Contrast dyes enhance the visibility of the developed images andfacilitate pattern alignment during manufacturing. Examples of contrastdye additives that may be used together with the light-sensitivemixtures of the present invention include Solvent Red 24 (C.I. No.26105), Basic Fuchsin (C.I. 42514), oil Blue N (C.I. No. 61555) andCalco Red A (C.I. No. 26125) up to ten percent weight levels, based onthe combined weight of resin and sensitizer.

Anti-striation agents level out the photoresist coating or film to auniform thickness. Anti-striation agents may be used up to five percentweight levels, based on the combined weight of resin and sensitizer. Onesuitable class of anti-striation agents is non-ionic silicon-modifiedpolymers. Non-ionic surfactants may also be used for this purpose,including, for example, nonylphenoxy poly(ethyleneoxy) ethanol;octylphenoxy (ethyleneoxy) ethanol; and dinonyl phenoxypoly(ethyleneoxy) ethanol.

Plasticizers improve the coating and adhesion properties of thephotoresist composition and better allow for the application of a thincoating or film of photoresist which is smooth and of uniform thicknessonto the substrate. Plasticizers which may be used include, for example,phosphoric acid tri-(B-chloroethyl)-ester; stearic acid; dicamphor;polypropylene; acetal resins; pbenoxy resins; and alkyl resins up to tenpercent weight levels, based on the combined weight of resin andsensitizer.

Speed enhancers tend to increase the solubility of the photoresistcoating in both the exposed and unexposed areas, and thus, they are usedin applications where speed of development is the overridingconsideration even though some degree of contrast may be sacrificed,i.e. in positive resists while the exposed areas of the photoresistcoating will be dissolved more quickly by the developer, the speedenhancers will also cause a larger loss of photoresist coating from theunexposed areas. Speed enhancers that may be used include, for example,picric acid, nicotinic acid or nitrocinnamic acid at weight levels of upto 20 percent, based on the combined weight of resin and sensitizer.

The prepared light-sensitive resist mixture, can be applied to asubstrate by any conventional method used in the photoresist art,including dipping, spraying, whirling and spin coating. When spincoating, for example, the resist mixture can be adjusted as to thepercentage of solids content in order to provide a coating of thedesired thickness given the type of spinning equipment and spin speedutilized and the amount of time allowed for the spinning process.Suitable substrates include silicon, aluminum or polymeric resins,silicon dioxide, doped silicon dioxide, silicon resins, galliumarsenide, silicon nitride, tantalum, copper, polysilicon, ceramics andaluminum/copper mixtures.

The photoresist coatings produced by the above described procedure areparticularly suitable for application to thermally grown silicon/silicondioxide-coated wafers such as are utilized in the production ofmicroprocessors and other miniaturized integrated circuit components. Analuminum/aluminum oxide wafer can be used as well. The substrate mayalso comprise various polymeric resins especially transparent polymerssuch as polyesters and polyolefins.

After the resist solution is coated onto the substrate, the coatedsubstrate is baked at approximately 70° C. to 125° C. untilsubstantially all the solvent has evaporated and only a uniformlight-sensitive coating remains on the substrate.

The coated substrate can then be exposed to radiation, especiallyultraviolet radiation, in any desired exposure pattern, produced by useof suitable masks, negatives, stencils, templates, and the like.Conventional imaging process or apparatus currently used in processingphotoresist-coated substrates may be employed with the presentinvention. In some instances, a post-exposure bake at a temperatureabout 10° C. higher than the soft bake temperature is used to enhanceimage quality and resolution.

The exposed resist-coated substrates are next developed in an aqueousalkaline developing solution. This solution is preferably agitated, forexample, by nitrogen gas agitation. Examples of aqueous alkalinedevelopers include aqueous solutions of tetramethylammonium hydroxide,sodium hydroxide, potassium hydroxide, ethanolamine, choline, sodiumphosphates, sodium carbonate, sodium metasilicate, and the like. Thepreferred developers for this invention are aqueous solutions of eitheralkali metal hydroxides, phosphates or silicates, or mixtures thereof,or tetramethylammonium hydroxide.

Alternative development techniques such as spray development or puddledevelopment, or combinations thereof, may also be used.

The substrates are allowed to remain in the developer until all of theresist coating has dissolved from the exposed areas. Normally,development times from about 10 seconds to about 3 minutes are employed.

After selective dissolution of the coated wafers in the developingsolution, they are preferably subjected to a deionized water rinse tofully remove the developer or any remaining undesired portions of thecoating and to stop further development. This rinsing operation (whichis part of the development process) may be followed by blow drying withfiltered air to remove excess water. A post-development beat treatmentor bake may then be employed to increase the coating's adhesion andchemical resistance to etching solutions and other substances. Thepost-development beat treatment can comprise the baking of the coatingand substrate below the coating's thermal deformation temperature.

In industrial applications, particularly in the manufacture ofmicrocircuitry units on silicon/silicon dioxide-type substrates, thedeveloped substrates may then be treated with a buffered, hydrofluoricacid etching solution or plasma gas etch. The resist compositions of thepresent invention are believed to be resistant to a wide variety of acidetching solutions or plasma gases and provide effective protection forthe resist-coated areas of the substrate.

Later, the remaining areas of the photoresist coating may be removedfrom the etched substrate surface by conventional photoresist strippingoperations.

The present invention is further described in detail by means of thefollowing Examples. All parts and percentages are by weight unlessexplicitly stated otherwise.

EXAMPLE 1 Synthesis of 5-Methylol-2,3,4-trihydroxybenzophenone Employing2.5 Hours Reaction Time at 40°-47° C.

2,3,4-Trihydroxybenzophenone (300 gm (1.3 moles)] was added to a 3liter, three neck flask equipped with mechanical agitation, athermometer, a condenser and an addition funnel. An aqueous solution ofsodium hydroxide [208 gm 98% by weight NAOH dissolved in 1 liter ofdistilled water (5.1 moles NaOH)l was added slowly to the flask. A darkaqueous solution of the trihydroxybenzophenone was formed rapidly. Aslight exotherm was observed causing the solution temperature to rise to˜48° C.

An aqueous 36.5% by weight formaldehyde solution [123.3 gm (1.5 moles)]was then added dropwise through the addition funnel at a controlled rateso not to cause the reaction temperature to exceed 50° C. Half theformaldehyde solution was added rapidly in five minutes and the secondhalf over a total of 80 minutes. After addition, the reaction wasallowed to proceed for an additional 80 minutes before it was acidifiedwith a dilute 37% aqueous hydrochloric acid solution by weight [513 gm(5.2 moles HCl)1. The change in the pH of the solution to a neutral orslightly acidic was associated with a change in its color to a yellowishorange.

The reaction solution was transferred to a larger container filled with3 liters of distilled water under vigorous agitation. The reactionsolution was dripped slowly into the agitated water over 30 minutesduration. A light solid precipitate was formed. The solid product wasfiltered out and dried in a vacuum oven at 50° C. for about 20 hours toremove substantially all water in the product.

The dried product weighed 306.5 gm which represented a 90.7% yield basedon a theoretical yield of 338 gm.

The structure of the above titled compound was confirmed by infraredspectral analysis and by proton NMR. The observed NMR ratio of thealiphatic hydrogens to the aromatic hydrogens was 0.296. Compared withthe theoretical ratio value of 0.33 for this compound the product purityis 87.99 by moles. High pressure liquid chromatography detected thepresence of approximately 7% by weight of trihydroxybenzophenonestarting material indicating that this was the major impurity.

EXAMPLE 2 Synthesis of 5-Methylol-2,3,4-trihydroxybenzophenone Employing2 Hours Reaction Time at 40°-45° C.

2,3,4-Trihydroxybenzophenone [300 gm (1.3 moles)] was added to a 3liter, three neck flask equipped with mechanical agitation, thermometer,a condenser and an addition funnel. An aqueous solution of sodiumhydroxide [208 gm 98% by weight NAOH dissolved in 1 liter of distilledwater (5.1 moles NAOH)] was added slowly to the flask. A dark aqueoussolution of the trihydroxybenzophenone was formed rapidly.

A slight exotherm was observed causing the solution temperature to riseto ˜45° C.

An aqueous 36.5% by weight formaldehyde solution [123.3 gm (1.5 moles)]was then added dropwise through the addition funnel at a controlled rateso not to cause the reaction temperature to exceed 50° C. Half theformaldehyde solution was added over a period of 70 minutes and thesecond half over a period of 110 minutes. The reaction solution waspoured into a larger container filled with 3 liters of distilled waterunder vigorous agitation. The reaction mixture was acidified with adilute 37% aqueous hydrochloric acid solution by weight (513 gm (5.2moles HCl)]. The change in the pH of the solution to a neutral orslightly acidic was associated with the precipitation of the product inthe form of a yellowish orange solid particle. The product was filteredout of solution and reslurried in fresh distilled water three times towash off trace acid as detected by the neutral pH of the last waterwash.

The product was dried in a vacuum oven at 50° C. for 24 hours to removesubstantially all water.

The dried product weighed 320 gm which represented a 94.7% yield basedon a theoretical yield of 338 gm.

The structure of the above titled compound was confirmed by infraredspectral analysis and by proton NMR. The observed NMR ratio of thealiphatic hydrogens to the aromatic hydrogens was 0.265. Compared withthe theoretical ratio value of 0.33 for this compound the product purityis 80.3 moles. High pressure liquid chromatography detected the presenceof 8.8% by weight of the trihydroxybenzophenone starting materialindicating that this was the major impurity.

COMPARISON 1 Synthesis of 5-Methylol-2,3,4-TrihydroxybenzophenoneEmploying 26 Hours Reaction Time And An Excess Of Formaldehyde

2,3,4-Trihydroxybenzophenone [200 gm (1.3 moles)] was added to a 3liter, three neck flask equipped with mechanical agitation, thermometer,a condenser and an addition funnel. An aqueous solution of sodiumhydroxide [106.5 gm 98% by weight NAOH dissolved in 690 gm of distilledwater (2.6 moles NaOH)] was added slowly to the flask. A dark aqueoussolution of the trihydroxybenzophenone was formed rapidly. A slightexotherm was observed causing the solution temperature to raise to ˜42°C.

An aqueous 36.5% by weight formaldehyde solution [147 gm (1.79 moles)]was added dropwise through the addition funnel in two parts. The firstportion of the formaldehyde solution [86 gm (1.05 moles)] was added overa period of 85 minutes. The reaction was then allowed to continue for 22hours at 40°-42° C. before adding the section portion of the remainingformaldehyde solution [61 gm (0.74 moles)] over a period of 70 minutes.Approximately 70 minutes later the reaction solution was poured into alarger container filled with 3.3 liters of distilled water undervigorous agitation.

The reaction mixture was acidified with glacial acetic acid solution(156 gm) added over a 2 hour period at 28° C. The change in the solutionacidity to a pH of 4 associated with the precipitation of the product inthe form of a yellowish orange solid particle. The product was filteredout of solution and dried in a vacuum oven at 50° C. for 24 hours toremove substantially all water.

The dried product weighed 199.4 gm which represented a 88.25% yieldbased on a theoretical yield of 226 gm.

The structure of the above titled compound was not confirmed by protonNMR analysis. The theoretical NMR ratio of the aliphatic hydrogens tothe aromatic hydrogens for this compound is 0.33. The observed NMR ratioof the product of this reaction was 0.08 suggesting a low puritymixture.

It is postulated that further condensation of the desired product intohigher oligmers may have formed under this extended reaction time and atthis higher formaldehyde level.

EXAMPLE 3 Mixed Cresol Novolak Synthesis Containing 10 Mole Percent Of5-Methylol-2,3,4-Trihydroxybenzophenone

A mixture of m-cresol [248.28 gm (2.3 moles)], p-cresol [165.5 gm (1.53moles)), a 37.8% aqueous solution of formaldehyde [228 gm (2.86 moles)]and oxalic acid dehydrate [1 gm (0.0081 moles)) was charged into a resinflask. The 1000 ml capacity resin flask used for this reaction wasequipped with a mechanical strirrer, a water cooled condenser, athermometer, an addition funnel, a nitrogen inlet valve and an adequateheating/cooling capacity. The reaction solution was heated up to 60° C.before the addition of the 5-methylol-2,3,4-trihydroxybenzophenoneproduct of Example 1 was started [100 gm dissolved in 285 mlmethanol/methoxy-acetoxypropane (about 0.38 moles). This solution wasadded to the reaction mixture through the addition funnel over a periodof 1.5 hours at a temperature range of 100°-83° C. The reaction wasallowed to continue at reflux temperature for another 1.5 hours beforestarting atmospheric distillation. The condenser was adjusted from thereflux vertical position to the horizontal distillation tilted positionand a receiving flask was installed at its end. The reaction temperaturewas raised up to 190° C. as the water and formaldehyde were removed. Atthis point 335.5 gm of aqueous distillate was collected in the receivingflask. The duration of the atmospheric distillation was about 2 hours.Vacuum was applied gradually to remove unreacted cresols. The maximumtemperature allowed during the vacuum distillation was 235° C. at 2mm/Hg of pressure. Most of the residual unreacted cresols were removedrapidly before applying full vacuum. It was necessary to hold fullvacuum for one hour and 40 minutes to insure the removal of essentiallyall unreacted cresol monomers. Nitrogen gas was used to equalize thepressure inside the flask and to avoid the oxidation of the moltennovolak. The novolak was poured into an aluminum tray under anatmosphere of nitrogen and was cooled to room temperature.

420 gm of solid novolak was collected containing less than 0.5% cresolmonomers by weight. The softening point of the novolak was 142.5°-143°C. determined by the ring and ball method, ASTM No. 06.03.

EXAMPLE 4 Mixed Cresol Novolak Synthesis Containing 5 Mole Percent Of5-Methylol-2,3,4-Trihydroxybenzophenone

A mixture of m-cresol [135.6 gm (1.25 moles)], p-cresol [90.6 gm (0.84moles)), a 37.7% aqueous solution of formaldehyde [46.6 gm (0.586moles)), oxalic acid dehydrate [1 gm (0.0081 moles)) and the5-methylol-2,3,4-trihydroxybenzophenone product of Example 1 [30 gm(about 0.13 moles)] were charged into a resin flask. The 1000 mlcapacity resin flask used for this reaction was equipped with amechanical stirrer, a water cooled condenser, a thermometer, a nitrogeninlet valve and an adequate heating/cooling capacity. The reactionsolution was heated up to reflux (99°-100° C.) and was allowed to reactfor three hours before starting atmospheric distillation. The condenserwas adjusted from the reflux vertical position to the horizontaldistillation tilted position and a receiving flask was installed at itsend. The reaction temperature was raised up to 175° C. as the water andformaldehyde were removed. At this point 93 gm of aqueous distillate wascollected in the receiving flask. The duration of the atmosphericdistillation was about 50 minutes.

Vacuum was applied gradually to remove unreacted cresols. The maximumtemperature allowed during the vacuum distillation was 215° C. at 2mm/Hg of pressure. Most of the residual unreacted cresols were removedrapidly before applying full vacuum, however, it was necessary to holdfull vacuum for 25 minutes to insure the removal of essentially allunreacted cresol monomers. Nitrogen gas was used to equalize thepressure inside the flask and to avoid the oxidation of the moltennovolak. The novolak was poured into an aluminum tray under anatmosphere of nitrogen and was cooled to room temperature. A total of 65gm of unreacted cresols was collected in the receiving flask at the endof the vacuum distillation. 216 gm of solid novolak was collectedcontaining less than 0.5% cresol monomers by weight. The softening pointof the novolak was 156° C. determined by the ring and ball method, ASTMNo. 06.03.

EXAMPLE 5 Mixed Cresol Novolak Synthesis Containing 7 Mole Percent Of5-Methylol-2,3,4-Trihydroxybenzophenone

A mixture of m-cresol [126 gm (1.17 moles)], p-cresol [84 gm (0.78moles)), a 36.5% aqueous solution of formaldehyde [121.5 gm (1.483moles)], oxalic acid dihydrate [1 gm (0.0081 moles)) and the5-methylol-2,3,4-trihydroxybenzophenone product of Example 1 [40 gm(about 0.13 moles)]were charged into a resin flask. The 1000 ml capacityresin flask used for this reaction was equipped with a mechanicalstirrer, a water cooled condenser, a thermometer, a nitrogen inlet valveand an adequate heating/cooling capacity. The reaction solution washeated up to reflux (98° C.) and was allowed to react for three hoursbefore starting atmospheric distillation. The condenser was adjustedfrom the reflux vertical position to the horizontal distillation tiltedposition and a receiving flask was installed at its end. The reactiontemperature was raised up to 200° C. as the water and formaldehyde wereremoved. The duration of the atmospheric distillation was 1.5 hours.Vacuum was applied gradually to remove unreacted cresols. The maximumtemperature allowed during the vacuum distillation was 227° C. at 2mm/Hg of pressure. Most of the residual unreacted cresols were removedrapidly before applying full vacuum. It was necessary to hold fullvacuum for 45 minutes to insure the removal of essentially all unreactedcresol monomers. Nitrogen gas was used to equalize the pressure insidethe flask and to avoid the oxidation of the molten novolak. The novolakwas poured into an aluminum tray under an atmosphere of nitrogen and wascooled to room temperature. 218 gm of solid novolak was collectedcontaining less than 0.5% cresol monomers by weight. The softening pointof the novolak was 160° C. determined by the ring and ball method, ASTMNo. 06.03.

COMPARISON 2 Mixed Cresol Novolak Synthesis With No5-Methylol-2l3l4-Trihydroxybenzophenone Added

A mixture of m-cresol [607.2 gm (5.62 moles)], p-cresol [404.8 gm (3.75moles)], a 37.75% aqueous solution of formaldehyde 1557 gm (7.03 moles)]and oxalic acid dehydrate [2 gm (0.0162 moles)] was charged into a resinflask. The 2000 ml capacity resin flask used for this reaction wasequipped with a mechanical stirrer, a water cooled condenser, athermometer, an addition funnel, a nitrogen inlet valve and an adequateheating/cooling capacity. The reaction solution was heated up to (100°C.) and was allowed to react at this reflux temperature for four hoursbefore starting the atmospheric distillation. The condenser was adjustedfrom the reflux vertical position to the horizontal distillation tiltedposition and a receiving flask was installed at its end. The reactiontemperature was raised up to 180° C. as the water and unreactedformaldehyde were removed. At this point 448.5 gm of aqueous distillatewas collected in the receiving flask. The duration of the atmosphericdistillation was about 2.5 hours. Vacuum was applied gradually to removeunreacted cresols. The maximum temperature allowed during the vacuumdistillation was 235° C. at 2 mm/Hg of pressure. Most of the residualunreacted cresols were removed rapidly before applying full vacuum. Itwas necessary to hold full vacuum for 1.5 hours to insure the removal ofessentially all unreacted cresol monomers. Nitrogen gas was used toequalize the pressure inside the flask and to avoid the oxidation of themolten novolak. The novolak was poured into an aluminum tray under anatmosphere of nitrogen and was cooled to room temperature.

838 gm of solid novolak was collected containing less than 0.5% cresolmonomers by weight. The softening point of the novolak was 157.5°-157°C. determined by the ring and ball method, ASTM No. 06.03.

COMPARISON 3 Mixed Cresol Novolak Synthesis With No5-Methylol-2,3,4-Trihydroxybenzophenone Added

This reaction was carried out in a 500 gallon reactor using a similarcresol mixture as in the above examples (60% m-cresol:40% p-cresol). Theformaldehyde molar ratio to cresols was 0.62. The total reaction timeemployed in this process was 18 hours. In addition, the total durationof the atmospheric distillation was approximately six hours and thevacuum distillation about four hours. The novolak was dissolved in ethylcellosolve acetate to form a 31.88% solution.

This novolak was isolated in the dry solid form by distilling off thesolvent from the solution (1887 gm solution) under vacuum attemperatures not exceeding 1600° C. in a similar manner to thatdescribed above. 710 gm of solid novolak was collected containing lessthan 0.5% cresol monomers by weight. The softening point of the novolakwas 135°-138° C. determined by the ring and ball method, ASTM No. 06.03.

Table I below provides dissolution times, softening points and relativeaverage molecular weight data of the novolaks prepared in Examples 3, 4,5 and Comparisons 2 and 3. The data in Table I shows that5-methylol-2,3,4-trihydroxybenzophenone-containing novolaks exhibitgreater solubilities in aqueous alkaline solutions than the comparisonmixed cresol novolaks having similar average molecular weights andsoftening points. In particular, Example 3 has a faster dissolution timethan Comparison 3 and Examples 4 and 5 have a faster dissolution timesthan Comparison 2. The dissolution times were measured for dry onemicron thick novolak coatings required to completely dissolve in anaqueous alkaline solution (HPRD-419 developer sold by Olin HuntSpecialty Products, Inc. of West Paterson, N.J.). Such coatings wereprepared from novolak solutions in ethyl cellosolve acetate atapproximately 25% solids content by means of spin coating. Silicon orsilicon dioxide wafers were used as the coating substrates. The spinspeeds employed using a Headway spinner were adjusted between 3000 to6000 RPM to provide equal one micron coatings for all the novolaksolutions according to variations in their solution viscosity as afunction of their average molecular weights. The coatings were dried ina Blue M hot air circulating oven at 100°-105° C. for thirty minutes.The average molecular weights (MW) and average molecular number (MN) ofthese novolaks were measured by gel permination chromatography (GPC)under the following conditions:

Column Set: 500, 100, 10,000, 100 and 40 Angstroms

Solvent: Tetrahydrofuran

Detector: Refractive Index

Flow Rate: 1.5 ml/min.

Injection Volume: 300 ml

Calibration: Polystyrene standards

                  TABLE I                                                         ______________________________________                                        Novolak                                                                       Example                        Molecular                                      or        Dissolution                                                                             Softening  Weight                                         Comparison                                                                              Time, Sec.                                                                              Point      MW    MN                                       ______________________________________                                        Example 3  5        143         3163 342                                      Example 4 68        156        19949 738                                      Example 5 20        160        16252 922                                      Comparison 2                                                                            260       157        16630 478                                      Comparison 3                                                                            10        138        not determined                                 ______________________________________                                    

EXAMPLE 6 Preparation of Resist Solution

Novolak prepared according to Example 3 (56 gm) was dissolved in anappropriate solvent (144 gm methoxyacetoxypropane) in a 400 mlcylindrical bottle rolled on a high-speed roller for approximately 20hours.

A portion of this solution (158.6 gm) was transferred into a 400 ml sizecylindrical amber-colored glass bottle. To this solution 11.375 gm ofthe photoactive compound and an additional solvent (27.9 gmmethoxyacetoxypropane) were added. The bottle was rolled on a high-speedroller for 12 hours at room temperature to dissolve all solids.

The photoactive sensitizer was prepared by reacting2,3,4-trihydroxybenzophenone with naphthoquinone(1,2)-diazide-5-sulphonyl chloride in a 1:2 molar ratio. The sensitizerresulting from this reaction is a mixture of the sulphono mono-, di- andtriesters with trihydroxybenzophenone as well as some unesterifiedtrihydroxybenzophenone.

The resulting resist solution was subsequently filtered through a 0.2 umpore-size filter using a millipore microfiltration system (100 ml barreland a 47 mm disk were used). The filtration was conducted in a nitrogenenvironment under a pressure of 30 pounds per square inch. Approximately180 ml resist solution was obtained.

EXAMPLE 7 Preparation of Resist Solution

Novolak prepared according to Example 4 (56 gm) was dissolved in anappropriate solvent (144 gm methoxyacetoxypropane) in a 400 mlcylindrical bottle rolled on a high-speed roller for approximately 20hours.

A portion of this solution (150 gm) was transferred into a 400 ml sizecylindrical amber-colored glass bottle. To this solution 10.65 gm of thephotoactive compound and an additional solvent (33.7 gmmethoxyacetoxypropane) were added. The bottle was rolled on a high-speedroller for 12 hours at room temperature to dissolve all solids.

The photoactive sensitizer was prepared by reacting2.3,4-trihydroxybenzophenone with naphthoquinone(1,2)-diazide-5-sulphonyl chloride in a 1:2 molar ratio. The sensitizerresulting from this reaction is a mixture of the sulphono mono-, di- andtriesters with trihydroxybenzophenone as well as some unesterifiedtrihydroxybenzophenone.

The resulting resist solution was subsequently filtered through a 0.2 umpore-size filter using a millipore microfiltration system (100 ml barreland a 47 mm disk were used). The filtration was conducted in a nitrogenenvironment under a pressure of 30 pounds per square inch. Approximately175 ml resist solution was obtained.

EXAMPLE 8 Preparation of Resist Solution

Novolak prepared according to Example 5 (30 gm) was dissolved in anappropriate solvent (70 gm ethyl lactate) in a 200 ml cylindrical bottlerolled on a high-speed roller for approximately 20 hours.

A portion of this solution (85 gm) was transferred into a 200 ml sizecylindrical amber-colored glass bottle. To this solution 6.375 gm of thephotoactive compound and an additional solvent (26.68 gm ethyl lactate)were added. The bottle was rolled on a high-speed roller for 12 hours atroom temperature to dissolve all solids.

The photoactive sensitizer was prepared by reacting2,3,4-trihydroxybenzopbenone with naphthoquinone(1,2)-diazide-5-sulphonyl chloride in a 1:2 molar ratio. The sensitizerresulting from this reaction is a mixture of the sulphono mono-, di- andtriesters with trihydroxybenzophenone as well as some unesterifiedtrihydroxybenzophenone.

The resulting resist solution was subsequently filtered through a 0.2 umpore-size filter using a millipore microfiltration system (100 ml barreland a 47 mm disk were used). The filtration was conducted in a nitrogenenvironment under a pressure of 30 pounds per square inch. Approximately100 ml resist solution was obtained.

COMPARISON 4 Preparation of Resist Solution

Novolak prepared according to Comparison 2 (98 gm) was dissolved in anappropriate solvent (252 gm methoxyacetoxypropane) in a 400 mlcylindrical bottle rolled on a high-speed roller for approximately 20hours.

A portion of this solution (300 gm) was transferred into a 400 ml sizecylindrical amber-colored glass bottle. To this solution 21.52 gm of thephotoactive compound and an additional solvent (67.37 gmmethoxyacetoxypropane) were added. The bottle was rolled on a high-speedroller for 12 hours at room temperature to dissolve all solids.

The photoactive sensitizer was prepared by reacting2,3,4-trihydroxybenzophenone with naphthoquinone(1,2)-diazide-5-sulphonyl chloride in a 1:2 molar ratio. The sensitizerresulting from this reaction is a mixture of the sulphono mono-, di- andtriesters with trihydroxybenzophenone as well as some unesterifiedtrihydroxybenzophenone.

The resulting resist solution was subsequently filtered through a 0.2 umpore-size filter using a millipore microfiltration system (100 ml barreland a 47 mm disk were used). The filtration was conducted in a nitrogenenvironment under a pressure of 30 pounds per square inch. Approximately380 ml resist solution was obtained.

COMPARISON 5 Preparation of Resist Solution

Novolak prepared according to Comparison 3 (98 gm) was dissolved in anappropriate solvent (252 gm methoxyacetoxypropane) in a 400 mlcylindrical bottle rolled on a high-speed roller for approximately 20hours.

A portion of this solution (300 gm) was transferred into a 400 ml sizecylindrical amber-colored glass bottle. To this solution 21.52 gm of thephotoactive compound and an additional solvent (46.9 gmmethoxyacetoxypropane) were added. The bottle was rolled on a high-speedroller for 12 hours at room temperature to dissolve all solids.

The photoactive sensitizer was prepared by reacting2.3,4-trihydroxybenzophenone with naphthoquinone(1,2)-diazide-5-sulphonyl chloride in a 1:2 molar ratio. The sensitizerresulting from this reaction is a mixture of the sulphono mono-, di- andtriesters with trihydroxybenzophenone as well as some unesterifiedtrihydroxybenzophenone.

The resulting resist solution was subsequently filtered through a 0.2 umpore-size filter using a millipore microfiltration system (100 ml barreland a 47 mm disk were used). The filtration was conducted in a nitrogenenvironment under a pressure of 30 pounds per square inch. Approximately350 ml resist solution was obtained.

PHOTORESIST PROCESSING Coating of Photoresist Composition onto aSubstrate

Photoresist solutions prepared in Examples 6, 7, 8 and Comparison 4 and5 were spin-coated with a spinner manufactured by Headway Research Inc.(Garland, Texas) onto a thermally grown silicon/silicon dioxide-coatedwafers of 10 cm (four inches) in diameter and 5000 angstroms in oxidethickness. Uniform coatings, after drying, of approximately 1.2 micronin thickness were obtained at spinning velocities ranging from 4,000 to7,000 RPM for 30 seconds. In order to obtain approximately identicalfilm thicknesses with all resist solutions, adjustments in the employedspin speed were necessary because of the variations in resistviscosities. Table II below provides the relationship between coatingfilm thickness and spin speed for all the resist samples.

                  TABLE II                                                        ______________________________________                                        Resin     Spin Speed ×                                                                        Film       Drying                                       Composition                                                                             1000 RPM    Thickness  Condition                                    ______________________________________                                        Example 6 4.0         1.23       100/105° C.,                                    5.0         1.08       30' oven                                     Example 7 6.5         1.21       100/105° C.                                                            30' oven                                     Example 8 4.0         1.35       100/105° C.                                     5.0         1.21       30' oven                                               7.0         1.02       30' oven                                               4.0         1.44       110/118° C.                                     5.0         1.31       50" Hot Plate                                Comparison 4                                                                            7.0         1.22       100/105° C.                                                            30' oven                                     Comparison 5                                                                            5.0         1.21       100/105° C.                                                            30' oven                                     ______________________________________                                    

The coated wafers were baked either in an air circulating convectionBlue M oven for 30 minutes at 100°-105° C. or on a hot plate for 50seconds at a temperature range from 110° to 118° C. The dry filmthicknesses were measured with a Sloan Dektak II surface profilometerunit.

Exposure of Coated Substrates

A Perkin-Elmer projection aligner model 340 Micralign was used toprovide adequate UV exposures of the above photoresist coatedsubstrates. The spectral output of this instrument covers the range from310 to 436 nanometers. The light intensity is monitored internally inthe instrument. The scan time was varied in order to provide differentexposure energies from which the resist sensitivity was determined. AHunt resolution chromium mask containing groups of lines and spaces,isolated lines and isolated spaces varying in dimensions with minimumfeatures of 1.25 microns.

The developed resist features were equal in their dimensions to maskfeatures at the optimum exposure energy.

An Ultratech step and repeat 1:1 projection unit, model Ultratech 1000with a 0.31 numerical aperture was used. This exposure tool provides anarrow spectral output of the G and H Hg lines (436-405 nm). Theinstrument produces high light intensity and short exposure timesmeasured in milliseconds and controlled accurately by the instrumentsensors and the shutter mechanism. Variable exposure energies were usedto determine optimum resist exposure energies required to reproduce maskfeatures. The mask used contained groups of lines and spaces, isolatedlines and spaces varying in their dimensions with a minimum feature sizeof 0.75 microns.

At optimum exposures the exposed resist image is completely removed byan optimum developer and the image dimension is equal to thecorresponding mask image dimension. Optimum developers can be differentfor each resist formulation. Such developers were determined byobtaining the maximum development contrast between the exposed and theunexposed resist areas where no resist film loss was detected in theunexposed resist areas.

Using the above noted mask featuring a group of equal lines and spacesallowed a quick determination of optimum resist exposure energy bymicroscopic examination of the developed resist images. The accuracy ofdetermining the optimum exposure by this method is within ±5 mJ/Cm².

Development of Exposed Resist Coated Substrates

A one minute immersion development process was used to develop exposedresist coatings. Two types of developers were employed, a metalcontaining sodium based developer and a tetramethylammonium hydroxidebased, metal ion free developer at different concentrations adjusted foreach resist system. The optimum developer concentration selected foreach resist provided the minimum unexposed film thickness loss of theresist coating while maximizing its development rate in the exposedareas, thus obtaining the highest development contrast for each system.The developers used and resist sensitivites are presented in Table III.

Immersion Development Process

The resist coated wafers produced and exposed according to the precedingdiscussions were placed on circular Teflon boats and immersed in twoliter Teflon containers filled with the appropriate developer (shown inTable III) for the duration of one minute. Agitation during thedevelopment was provided by means of nitrogen bubbling distributedevenly throughout the tank. Upon removal the wafers were rinsed indistilled water for one minute and blown dry under a stream of nitrogengas.

Table III below provides the developers employed in processing resistsamples of Examples 6, 7, 8 and Comparisons 4 and 5 as well as theresulting resist sensitivities. Waycoat Positive LSI Developer ("LSI")sold by Olin Hunt Specialty Products is a metal ion containing developerand was used diluted with distilled water as indicated in Table III. Themetal ion free developer Waycoat MIF Developer ("MIF") is also sold byOlin Hunt Specialty Products, was used diluted with distilled water atthe concentrations indicated in Table III below.

                  TABLE III                                                       ______________________________________                                                   Developer        Resist                                                       Concentration    Sensitivity                                       Resist     % LSI       % MIF    mJ/Cm.sup.2                                   ______________________________________                                        Example 6  20                   87-94                                         Example 7  28                   260                                                      39.5                 155                                                      50                   117                                                      62                    78                                                      70                   47-60                                         Example 8  42                   150                                                                  30       230                                                                  32       170                                           Comparison 4                                                                             70                    93                                                                  39       155                                           Comparison 5                                                                             33                    58                                                                  25.5      71                                           ______________________________________                                    

Resist Image Quality & Thermal Deformation Measurements A. Image Quality

The quality of resist images were examined after development and priorto the hard baking step. Optical microscopic examination as well aselectron scan microscopy were used. The qualitative evaluation of resistimages was based on the sharpness of the upper edges of resist lines andspaces, the steepness of their profiles and the smoothness of the resistimage surfaces. The slope of the vertical line connecting the top edgeof the resist image with its bottom edge was used to quantitativelydescribe the steepness of the side wall profile.

In general, low molecular weight novolaks produce better quality resistimages. This was also true for the resist systems of this invention.However, resist image quality compared at both low and high molecularweight based novolaks showed better results with novolak systems of thisinvention over those made with corresponding comparison novolak. Thiscomparison is provided in Tables IV and V below.

                  TABLE IV                                                        ______________________________________                                        Low Molecular Weight Novolak Based Resist Systems                                       IMAGE QUALITY                                                                   Slope     Definition of                                           Resist      Angle     Top Edge    Surface                                     ______________________________________                                        Example 6   89-90°                                                                           Very Sharp  Smooth                                      Comparison 5                                                                              85-89°                                                                           Sharp       Smooth                                      ______________________________________                                    

                  TABLE V                                                         ______________________________________                                        High Molecular Weight Novolak Based Resist Systems                                        IMAGE QUALITY                                                                   Slope    Definition of                                          Resist        Angle    Top Edge    Surface                                    ______________________________________                                        Example 7                                                                     Mild developers                                                                             85°                                                                             Sharp       Smooth                                     (39.5%, 50%                                                                   and 62% LSI)                                                                  Aggressive    85°                                                                             Poor        Rough                                      developer     poor                                                            (70% LSI)                                                                     Example 8                                                                     Mild developers                                                                             85-89°                                                                          Very Sharp  Smooth                                     (42% LSI and                                                                  30% MIF)                                                                      Comparison 4                                                                  Mild developers                                                                             85°                                                                             Poor        Smooth                                     (39.5%, 50%   poor                                                            and 62% LSI)                                                                  Aggressive    85°                                                                             Poor        Rough                                      developer     poor                                                            (70% LSI)                                                                     ______________________________________                                    

B. Thermal Deformation

The developed resist images were hard baked in a convection, aircirculating Blue M oven at 130° C. for 30 minutese after which theresist images were examined for distortion and thermal flow. Thisexamination was carried out by means of optical microscopy and scanelectron microscopy. An additional 30 minutes hard bake at 150° C. wasapplied only to resist images showing no thermal deformation or flowafter the first 130° C. hard bake.

The resist thermal image deformation was described by the rounding ofthe image top edges and the decrease in its profile steepness. Theseobservations were more pronounced at the edges of large resist areasthan small lines.

Resist systems based on the novolaks of this invention exhibited betterresistance to thermal flow than the comparison system as shown in TableVI below.

                  TABLE VI                                                        ______________________________________                                                Thermal Image Deformation                                                     130° C.                                                                             150° C.                                                     Edge     Decreased Edge   Decreased                                 RESIST    Rounding Slope     Rounding                                                                             Slope                                     ______________________________________                                        Example 7 No       Slight    Yes    Yes                                       Example 8 No       No        No     Yes                                       Comparison 4                                                                            Yes      Yes       Yes    Yes                                       ______________________________________                                    

What is claimed is:
 1. The process of forming an positive image on aphotoresist-coated substrate comprising:(1) coating said substrate witha light-sensitive composition useful as a positive working photoresist,said composition comprising an admixture of o-quinonediazide compoundand a binder resin comprising the condensation reaction of precursorscomprising para-cresol, meta-cresol, formaldehyde, and amethylol-substituted trihydroxybenzophenone having formula (I): ##STR9##and said binder resin containing units of formula (II): ##STR10##wherein the starting mole ratio of meta-cresol to para-cresol is fromabout 70:30 to about 30:70; wherein the starting mole ratio of saidmethylol-substituted trihydroxybenzophenone to the other phenolicprecursors is from 0.1:99.9 to 20:80; and wherein said resin has fromabout 0.1% to about 30% by moles of the units of formula (II); theamount of said o-quinonediazide compound being about 5% to about 40% byweight and the amount of said binder resin being about 60% to 95% byweight, based on the total solid content of said light-sensitivecomposition; (2) subjecting said coating on said substrate to animage-wise exposure of radiant light energy; and (3) subjecting saidimage-wise exposed coated substrate to a developing solution wherein theexposed areas of said light-exposed coating are dissolved and removedfrom the substrate, thereby resulting in positive image-wise pattern inthe coating.
 2. The process of claim 1 wherein said radiant light energyis ultraviolet light.
 3. The process of claim 1 wherein said developingsolution comprises an aqueous solution of an alkali metal hydroxide orsilicates or an aqueous solution of tetramethylammonium hydroxide. 4.The process of claim 1 wherein said units of formula (II) representabout 5% to about 10% by moles of said binder resin.
 5. The process ofclaim 1 wherein said methylol-substituted trihydroxybenzophenone is5-methylol-2,3,4-trihydroxybenzophenone.
 6. The process of claim 1wherein the mole ratio of the methylol-substitutedtrihydroxybenzophenone to the total of the other phenolic compounds isfrom about 5:95 to about 10:90.
 7. The process of claim 1 wherein themole ratio of formaldehyde to total phenolic compounds is less thanabout 1:1.